Mobility control in oil recovery processes

ABSTRACT

Improved secondary and tertiary recovery processes wherein a mobility buffer is used are improved by alternately injecting mobility buffer slugs (containing mobility reducing agents) and slugs of water followed by a driving agent. For example, improved crude oil recoveries with emulsion and micellar systems are obtained by alternately injecting aqueous slugs containing mobility reducing agents and slugs of water followed by drive water to displace the system through the reservoir. The mobility buffer slugs can have progressively decreasing concentrations of the mobility reducing agent relative to the initial mobility buffer slug.

P11 7912 OR 39617018183 umtea Ib'IaleS l'atCllt [15] 3,670,818

Knight 1 June 20, 1972 [s41 MOBILITY CONTROL IN OIL 2,927,637 3/1960Draper ..l66/273 RECOVERY PROCESSES 3,039,529 6/1962 McKennon 16'6/2753,261,399 7 1966 C l ..l66 273 [72] Inventor: Bruce L. Knight,Littleton, Colo. oppe [73] Assignee: Marathon Oil Company, Findlay, OhioPrimary Examiner-Stephen J. Novosad Filed: April 1970fittltzirztnelym-e-iloseph C. Hernng, Richard C. Wlllson, Jr. and Jack[2]] Appl. No.: 33,021

[ ABSTRACT [52] U.S. Cl ..l66/273, 166/274 Improved secondary andtertiary recovery processes wherein [51] Int. Cl ..E2lb 43/22 a mobilitybufi'er is used are improved by alternately injecting [58] Field ofSearch ..l66/273, 274, 275, 305 R, mobility buffer slugs (containingmobility reducing agents) D and slugs of water followed by a drivingagent. For example,

' improved crude oil recoveries with emulsion and micellar [56]Rem'ence' and systems are obtained by alternately injecting aqueousslugs UNITED STATES PATENTS containing mobility reducing agents andslugs of water followed by dnve water to displace the system through thereser- 3,406,754 10/ l 968 Gogarty 166/273 oir, Th mobilit buffer slugscan have progressively decreas- 2,827,964 3/ ing concentrations of themobility reducing agent relative to 2,341 ,500 2/1944 Detling 166/274 UXthe i i i mobility b ff slug 2,731,414 1! 1956 Binder, Jr. et a1...l66/274 3,308,883 3/1967 Foster 166/275 12 Claims, 1 Drawing FigureOIL RECOVERY v5 TOTAL POLYMER lNJECTED TOTAL OIL RECOVERY 0g TOTALPOLYMER INJECTED (00!: volume X ppm PATENTEDmzo I972 3, 670 8 l 8 OILRECOVERY vs TOTAL POLYMER lNJECTED 9O Curve b r 5 70 l 5 6O J 8 LU 50 0C|Curve C] a 40 O i 30 I P ,9 20

TOTAL POLYMER INJECTED (pore volume x ppm) INVENTOI? BRUCE L. KNIGHTATTORNEY MOBILITY CONTROL IN OIL RECOVERY PROCESSES BACKGROUND OF THEINVENTION 1. Field of the Invention.

This invention relates to recovering crude oil form a subterraneanreservoir having an injection means in fluid communication with aproduction means and wherein a flooding agent is injected followed by amobility reducing agent and this, in turn, followed by drive water.

2. Description of the Prior Art.

It is known in the prior art that emulsions and micellar solutions andmiscible agents such as alcohols, ketones, aldehydes, and likematerials, optionally dissolved in aqueous or hydrocarbon systems, andsurfactants (dissolved in aqueous or non-aqueous systems) are useful torecover crude oil from a subterranean reservoir. Mobility control isimportant is secondary or tertiary recovery processes using theseagents. Mobility control is obtained by following the primary slug witha slug containing a mobility reducing agent, e.g., an aqueous solutioncontaining a partially hydrolyzed, high molecular weight polyacrylamide,polysaccharide, natural polymer, synthesized polymers, etc. Thereafter,the mobility buffer slug is followed by a drive material such ashydrocarbon or water to displace the system through the reservoir. Crudeoil is recovered through a production means in fluid communication withthe reservoir.

Examples of flooding processes are taught in U.S. Pat. No. 3,497,006 toJones et a]. and U.S. Pat. No. 3,254,714 to Gogarty et al. These patentsteach that a micellar dispersion is injected into a reservoir, followedby a mobility reducing agent and this, in turn, followed by a drivewater. The micellar dispersion performs like a miscible-type floodingagent to recover up to 100 percent of the oil.

In the use of mobility reducing agents within mobility buffer slugs toimprove the flooding characteristics and protect against fingering, itis generally accepted that the primary displacing slug be followed by aslug of water containing the mobility reducing agent and this, in turn,followed by a drive water. The slug containing the mobility reducingagent can have graded mobilities therein to give improved floodingcharacteristics.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING The FIGUREindicates the amount of tertiary oil recovery vs. the total polymerinjected [total polymer injected is obtained by multiplying thefractional pore volume of polymer solution times the polymer solutionconcentration defined as ppm. (parts per million)]. A constantfractional pore volume of micellar solution is injected for the twocurves. Curve a illustrates the amount of tertiary oil recovered byfollowing a micellar solution with one bank of aqueous slug containing aconstant composition of partially hydrolyzed, high molecular weightpolyacrylamide. Curve b represents the amount of tertiary oil recoveryby following a micellar solution (same volume and identical solution asused in Curve with multiple alternate slugs of aqueous solutions firstcontaining partially hydrolyzed, high molecular weight polyacrylamideand then slugs of water. The difference in oil recoveries between Curvesa and b is an indication of the increased or improved effectiveness ofmultiple alternate slugs of mobility bufi'er and water as taught by thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A displacing fluid may precedethe initial mobility bufler slug. Examples of displacing fluids includeboth miscible and immiscible systems and those fluids havingcharacteristics of both. Specific examples of displacing fluids includeoil-external and water-extemal emulsions, oil-extemal and water-externalmicellar dispersion, anhydrous soluble oils, nonaqueous and aqueousmediums containing agents to reduce interfacial tension betweenhydrocarbon and water, e.g., alcohols, aldehydes, surfactants, ketones,etc., and like materials. Specific examples of useful displacingmaterials include those defined in U.S. Pat. Nos. 3,254,714 and3,467,187 to Gogarty et al.; and U.S. Pat. No. 3,497,006 to Jones et al.The displacing fluid can be composed of similar or dissimilar fluidsinjected separately and can be liquid, foam, combinations of liquid andfoam, etc.

The mobility buffer is substantially aqueous. It contains sufficientmobility reducing agent to substantially reduce the mobility of thewater. Any mobility reducing agent is useful with this invention as longas the agent efl'ectively reduces the relative mobility of the fluidflowing in the reservoir. Examples of useful mobility reducing agentsinclude polysaccharides, partially hydrolyzed high molecular weightpolyacrylamides such as the Pusher polymers sold by Dow ChemicalCompany, Midland, Michigan, naturally occurring high molecular weightpolymers and synthesized high molecular weight polymers, copolymers,terpolymers, etc. The mobility buffer can contain other additives suchas bactericides, corrosion inhibiting agents, etc. Also, the mobilitybufier can contain electrolytes, preferably compatible with the ionswithin the formation.

The mobility bufier is followed by a drive material which can be aqueousor non-aqueous but which is preferably aqueous. The drive material cancontain electrolytes or salts, but preferably the electrolytes arecompatible with the salts within the subterranean formation.

The initial slug of mobility buffer is small, but preferably has ahigher concentration of mobility bufi'er agent relative to thesubsequent slugs of mobility buffer. The size of the mobility bufferslug is preferably less than about 25 percent of the formation porevolume, and more preferably at least about 5 percent and less than 15percent pore volume. This initial slug is followed by alternate waterslugs and mobility bufler slugs, the latter usually containing lesseramounts of mobility reducing agents. After the last desired slug ofmobility buffer is injected, drive water is injected to displace theflooding fluids through the reservoir.

The subsequent volumes of mobility buffer are generally smaller involume, as mentioned earlier, and can contain lesser concentrations ofmobility reducing agent. However, mobility bufier slugs constant involume and concentration give good results.

The volume of water slug injected after each mobility bufier slug ispreferably less than about 25 percent fonnation pore volume and morepreferably at least about 5 percent and less than 15 percent porevolume.

At least two mobility buffer slugs are injected and preferably at leastfour slugs are injected. Each slug is followed by a water slug exceptthe last one and then drive water is continuously injected.

The following example is presented to teach specific working embodimentsof the invention. Unless otherwise specified, the percents are based onvolume:

EXAMPLE 1 Berea sandstone cores 4 feet long by 3 inches in diameter aresaturated with water, then flooded with crude oil to irreducible watersaturation and thereafier flooded with water to residual oil saturation.The cores are flooded with 2 percent formation volume of identicalmicellar dispersion followed by alternate slugs of water containing DowPusher No 700 (a high molecular weight, partially hydrolyzedpolyacrylamide marketed by Dow Chemical Company, Midland, Michigan), andwater. The concentration of Pusher within each slug of mobility bufferis expressed in ppm, i.e., parts per million. The residual oilsaturations of the cores, the total polymer injected,

the ultimate oil recovered, etc. are indicated in Table 1:

TABLE 1 EFFECT OF POLYMER INJECTION SCHEME ON TERTIARY OlL RECOVERYTotal Residual polymer oil saturainjectod, tion, be- Oil PVX [ore floodrecovered it 1111 lnjnutml scheme (percent formation pore volume, andp.p.m.) p.p.m. porconl. purccnl. 13",, (1,000 ,5 at ),40% (125 p. .m.),(water) 100 535.0 72. I 747 0100), (32105, 5 (2 60), 5% (water), 5%(200), 5% (water). 5% (200), 6% (water), 5% (200), (wator) 1 04 58. 108. H 0100 5% (water), (600), 10% (water), 5% (400), (water) 220 35 110;. 7 4 5% (1,200), 6% (water), 20% (800) 10% (water), 10% (400),(water) H. 260 30. l 5 11% 11,200); 5% (water), 20% (800), 5% (water),30% (600). (water) 406 35. 7 SJ. 0 '5 5",, (3,000), 5% (water), 10%(1,000), 5% (water), 20% (500), 5% (water), 40% (400), 5% (water), 35%(100), 545 37 4 90 6 7 20% (2,500), 10% (water), 30% (800), 10% (water),10% (100), (water) 750 38.6 00.1

Drive water is injected until no more oil is produced at end of cure.

it is not intended that the invention be limited by the above example.Rather, all equivalents obvious to those skilled in the art are intendedto be included within the scope of the invention as defined in thespecification and appended claims.

What is claimed is:

1. In a process of recovering crude oil from a subterranean formationcomprised of injecting into the formation a mobility buffer comprised ofan aqueous solution containing mobility reducing agent and displacing itwith drive water toward a production means in fluid communication withthe formation to recover crude oil through the production means, theimprovement comprising:

I injecting 5 percent up to about percent formation pore volume of themobility buffer, followed by 2. 5 percent up to about 25 percentformation pore volume of drive water, and

3. repeating step 1 at least once, and

4. then injecting sufficient drive water to displace the mobility buffertoward the production means.

2. The process of claim 1 wherein a displacing agent precedes themobility buffer slug.

3. The process of claim 2 wherein the displacing agent is selected fromthe group consisting of immiscible agents, miscible agents, and agentshaving both immiscible and miscible characteristics.

4. The process of claim 3 wherein the displacing agent is selected fromthe group consisting of emulsions and micellar dispersions.

5. The process of claim 1 wherein the mobility reducing agent is apartially hydrolyzed high molecular weight polyacrylamide.

6. The process of claim 1 wherein steps (1) and (2) are repeated atleast twice.

7. The process of claim 1 wherein the formation pore volumes in (l and(2) are about 5 percent up to about 15 performation comprised ofinjecting into the formation a micellar dispersion followed by amobility buffer comprised of an aqueous solution containing mobilityreducing agent and wherein the micellar dispersion and mobility bufferare displaced toward a production means in fluid communication with theformation to recover crude oil through the production means,

the improvement comprising displacing the micellar dispersion andmobility bufier by:

l. injecting about 5 percent to about 25 percent formation pore volumeof a mobility bufier followed by 2. about 5 percent to about 25 percentformation pore volume of a water drive,

3. repeating ste l at least once, and

4. then injecting suflicient drive water to displace the previouslyinjected slugs toward the production means.

10. The process of claim 9 wherein the mobility reducing agent is apartially hydrolyzed, high molecular weight acrylamide.

11. The process of claim 9 wherein steps (1) and (2) are repeated atleast twice.

12. The process of claim 9 wherein the formation pore volume in steps land 2) is about 5 percent to about 15 percent formation pore volume.

2. The process of claim 1 wherein a displacing agent precedes themobility buffer slug.
 2. 5 percent up to about 25 percent formation porevolume of drive water, and
 2. then injecting sufficient drive water todisplace the mobility buffer toward the production means.
 2. about 5percent to about 25 percent formation pore volume of a water drive, 3.repeating step (1) at least once, and
 3. repeating step (1) at leastonce, and
 3. The process of claim 2 wherein the displacing agent isselected from the group consisting of immiscible agents, miscibleagents, and agents having both immiscible and miscible characteristics.4. The process of claim 3 wherein the displacing agent is selected fromthe group consisting of emulsions and micellar dispersions.
 4. theninjecting sufficient drive water to displace the mobility buffer towardthe production means.
 4. then injecting sufficient drive water todisplace the previously injected slugs toward the production means. 5.The process of claim 1 wherein the mobility reducing agent is apartially hydrolyzed high molecular weight polyacrylamide.
 6. Theprocess of claim 1 wherein steps (1) and (2) are repeated at leasttwice.
 7. The process of claim 1 wherein the formation pore volumes in(1) and (2) are about 5 percent up to about 15 percent.
 8. In a processof recovering crude oil from a subterranean formation comprised ofinjecting into the formation a mobility buffer comprised of an aqueoussolution containing mobility reducing agent and displacing it with drivewater toward a production means in fluid communication with theformation to recover crude oil through the production means, theimprovement comprising:
 9. In a process for recovering crude oil from asubterranean formation comprised of injecting into the formation amicellar dispersion followed by a mobility buffer comprised of anaqueous solution containing mobility reducing agent and wherein themicellar dispersion and mobility buffer are displaced toward aproduction means in fluid communication with the formation to recovercrude oil through the production means, the improvement comprisingdisplacing the micellar dispersion and mobility buffer by:
 10. Theprocess of claim 9 wherein the mobility reducing agent is a partiallyhydrolyzed, high molecular weight acrylamide.
 11. The process of claim 9wherein steps (1) and (2) are repeated at least twice.
 12. The processof claim 9 wherein the formation pore volume in steps (1) and (2) isabout 5 percent to about 15 percent formation pore volume.